Microstructure Evolution And In-situ Mechanical Property Of Cu-Sn Compounds In Micro Solder Joint

With the development of power electronic technology,the third generation semiconductor(such as SiC)power devices have many outstanding advantages,such as big bandgap,high breakdown voltage,high electron drift velocity,which draw people’s attention.However,the traditional Sn-based solder can not meet the requirement of high temperature opreating in power devices.Recently,to form full intermetallic compounds is a hot topic,which can solve the problem for high temperature packaging connection.To study the IMC’s formation law and to reveal the IMC’s formation mechanism are very significant to engineering and theoretical value for designing the coating thickness.This paper is foucused on the microstructure evolution and in-situ mechanical property of Cu-Sn compounds in micro solder joint.It obtains the Cu/Sn solid-liquid interface reaction,the effect of master element(Sn/Cu thickness ratio)on Cu/Sn interfacial intermetallic compound transformation law and the mechanical properties of Cu-Sn intermetallic compounds at different temperature.Moreover,a new method for fabricating full Cu3Sn solder joint efficiently and quickly by thermal compression heating is proposed.The growth kinetics of interfacial Cu-Sn intermetallic compound at the solid Cu/liquid Sn interface is investigated in 240-270℃ by reflowing.It obtains Cu/Sn solid-liquid interface Cu6Sn5 growth index(Cu6Sn5 layer growth rate per unit time)and Cu6Sn5 grain coarsening index(Cu6Sn5 grain coarsening rate per unit time)in 5-190s at 260 ℃,the mathematical expression of initial Cu3Sn formation time and temperature,interfacial compound layer thickness at 240-270 ℃.The effect of master element on the Cu3Sn layer thickness of Sn/Cu6Sn5/Cu3Sn/Cu interface was investigated.When Cu is the mater element,the Cu3Sn layer thickness shows linear decay with the increasing aging time.When Sn is the mater element,the Cu3Sn layer thickness increased linearly with the square root of aging time.The effect of temperature on the microstructure evolution patterns of Cu3Sn layer thickness for Sn/Cu6Sn5/Cu3Sn/Cu interface is investigated.When the Cu element is the master element,the consumption rate of Cu3Sn layer is parabolic with the aging temperature.When the master element is Sn,the growth rate of Cu3Sn layer shows parabolic law with the aging temperature.The mechanical properties of Cu-Sn intermetallic compounds are investigated by nanoindentation at elevated temperature.The constitutive equations of hardness,elastic modulus and plasticity of interfacial compounds Cu6Sn5 and Cu3Sn at different temperatures are obtained.The hardness of Cu6Sn5 and Cu3Sn obeys the linearly decay with the elevated temperature.The elastic modulus of Cu6Sn5 and Cu3Sn and temperature obey parabolic law during 25-200 ℃.The relationship between plasticity factor of interfacial compound and temperature obeys parabolic law.The fast formation of Cu3Sn solder joints are investigated by induction heating process.Compared with reflowing,the introducing of induction heating process showed benefit effects on enhancing the interfacial reaction at the liquid Sn/solid Cu metallization interface,the full Cu3Sn solder joint can be obtained in a few minutes.It reveals the interfacial microstructure evolution mechanism and establishes the interfacial intermetallic compound growth and evolution model.The faster formation of Cu3Sn solder joint can be fabricated by thermal compression bonding.Compared with induction heating process,the temperature gradient caused by compression bonding contributes to enhancing the interfacial reaction at the liquid Sn/solid Cu metallization interface,the full Cu3Sn solder joint can be obtained in 10 seconds.It reveals the interfacial microstructure evolution mechanism under temperature gradient.It establishes the interfacial compound growth and evolution model under temperature gradient.